Change in the Main Trends of Pedogenesis during Final Stages of the Late Pleistocene in the Western Sector of Beringia

In sediments of the ice complex (yedoma) of MIS-3 and MIS-2 ages formed in the Late Pleistocene on the territory of the western sector of Beringia, the presence of four buried soils has been established. The main material of the sediments is represented by cryopedoliths—frozen mineral sediments of silty or silty–sandy composition, which passed through the stage of synlithogenic pedogenesis in the course of their accumulation and preserve certain signs of pedogenesis, but not fully formed soil profiles. Synlithogenic pedogenesis occurred under severe winter conditions, with high summer heat supply and sufficient moisture in the uppermost layers of the forming soils. It was limited to the active mineralization of the most easily decomposable organic residues with the release of a significant amount of nutrients and burial of plant residues in the form of detritus resistant to biochemical transformation in the middle and lower parts of the profiles. In MIS-3, synlithogenic soil formation was periodically interrupted by epigenetic soil formation caused by climatic warming with an increase in the depth of seasonal thawing and soil moistening, a cessation or sharp weakening of the supply of mineral sediment to the surface, and restructuring of the landscape situation. The soils formed at the beginning of MIS-3 are characterized by the greatest diversity of their morphologies and degree of profile development. The two subsequent soils, belonging to the middle stage of MIS-3, bear traces of hydromorphic or semihydromorphic pedogenesis and are close to the soils of modern swampy tundra. The soils of the final stage of MIS-3 developed under conditions of increasing climate severity and supply of mineral sediments to the surface. There are no signs of epigenetic soil formation in the MIS-2 strata.